Morning All

Over the course of a few runs I have noticed a clear discrepancy between what I have recorded using my Garmin Edge 810 and what my friend has recorded using the Strava app on his mobile phone.

Garmin vs Strava (km):

5.53 vs 6.49

6.75 vs 8.14

5.10 vs 6.49

10.31 vs 10.89*

Is there a particular reason for this, would the Garmin be a more accurate measure given that its a GPS device rather then a phone or has this no bearing at all? For clarity both using the same start/stop point.

* This run should definitely be longer on the Garmin as I ran an extra .5k to bring up an even 5k while my friend was having a “comfort break.”

Katie’s Lezyne seems to consistently read about 10% under on distance compared to my Garmin 130.

Phone’s typically seem to give worse accuracy – you definitely seem to get more ‘out there’ segment timings tracking on a phone and also missed segments (which makes me think accuracy might be worse).  I don’t know what info Strava has access to – in theory the phone should be better as it can use mobile masts to improve accuracy (Google uses wifi networks as well i think).

How do you run with your 810?  Does it have a clear view of the sky? (How does your route look – smooth or jerky, as though it’s dropping signal)

I run with it in my hand and going by the routes posted on Strava they all appear to be smooth.  I had issues with strava on my phone misbehaving and considered the Garmin would be more accurate hence using it for running.

Had wondered if it might be auto pausing so have switched that off but still get discrepancies.

Its hardly the end of the world merely curious as to what could be causing it.  i have a 235 turning up next week so will be interesting to see a side by side comparison.

Download both GPX files and compare them side by side on real map and see which one deviates most from actual paths.

some garmin devices use both the american and the russian satellites. you can also set recording for every second or ‘smart’. These different recording protocols may make a difference.

Lots of differences, much down to sampling rates, plus a phone GPS may be more tuned to nagivation than tracking. Where the devices are kept also makes a difference. Clear line of sight of the satellites is important as is a good lock on lots of them. Phones can do navigation with a limited lock and will snap to a road on a map so accuracy isn’t so important.

A Garmin can also use a wheel speed sensor which will track actual ground distance, though you need the sensor fitted to the wheel. They usually have a barometer which can be more accurate with altitude, though you really need to calibrate them. A phone via Strava will use mapping data to correct altitude, though it’s based on known altitude in a grid square.

The use of mobile masts is to mainly provide a fast lock. GPS lock requires downloading known satellite positions and other data. It’s slow from the satellites but quick via mobile data. Phones can do basic positioning from the masts also on the absence of a GPS lock but it’s not accurate.

Makes sure Garmin is set to record every second, smart isn’t that smart as it requires definite changes in direction and speed to record, so a constant 5mph in a long meander of s-bends could have start and end only recorded so a straight line reducing distance.

barometer which can be more accurate with altitude, though you really need to calibrate them

unless you have a 130 where Garmin have given no way of calibrating the barometer so actually its much less accurate than using satellites and “current elevation” is often nonsense (i’m Sure my home isnt 60m below sea level)

Also bear in mind that elevation measurement is also sometime problematic. I think you need 3 satellites for a good tracking lock but you need 4 for a good elevation reading.

Some GPS watches/trackers that use barometric pressure can at least be sometimes changed in settings, most systems that just use GPS based systems relies on the earth not getting in the way of the satellites…

barometric is a bag of pish.

two garmin edge 500s with barometric next to each other would record +- 2-300 meters spot height out at any given time and by the end of the day could be +- 2000m out from each other …. and it was random as to which was higher or lower…. when we rode over canada.

When we plugged them into strava , strava agreed the data was shite an over wrote it with what the map says as the figures in strava were the same.

makes you wonder what good barometric data is if the recording programs just ignore it anyway.

tbh they are all not that accurate. for example if you want to get a good strava time use a phone!

I use my garmin.

if you want to get a good strava time use a phone!

Totally, you are only ever one bad GPS point away from a KOM 😀

yup.

a lot of the downhill kom’s near me are down to gps issues. the strava plots show straight lines down hills etc. even going backwards 🙂

The likes of a Garmin is more accurate.  I’ve been with friends using phone apps and there are differences. I’ve also tried it myself running both together over a strava segment – the garmin was more accurate.

Do you have auto pause enabled on your Garmin? It can “jump” straight between 2 points missing out some distance during a pause, if your speed drops below the threshold.

Garmin GPS is sometimes not that great if your route is very twisty; on, e.g., forest singletrack, I see a large discrepancy using the wheel speed sensor vs. using just GPS.